warning[E0713]: borrow may still be in use when destructor runs
  --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:53:5
   |
LL | fn scribbled<'a>(s: Scribble<'a>) -> &'a mut u32 {
   |              -- lifetime `'a` defined here
LL |     &mut *s.0 //[nll]~ ERROR borrow may still be in use when destructor runs [E0713]
   |     ^^^^^^^^^ returning this value requires that `*s.0` is borrowed for `'a`
...
LL | }
   | - here, drop of `s` needs exclusive access to `*s.0`, because the type `Scribble<'_>` implements the `Drop` trait
   |
   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future

warning[E0713]: borrow may still be in use when destructor runs
  --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:64:5
   |
LL | fn boxed_scribbled<'a>(s: Box<Scribble<'a>>) -> &'a mut u32 {
   |                    -- lifetime `'a` defined here
LL |     &mut *(*s).0 //[nll]~ ERROR borrow may still be in use when destructor runs [E0713]
   |     ^^^^^^^^^^^^ returning this value requires that `*s.0` is borrowed for `'a`
...
LL | }
   | - here, drop of `s` needs exclusive access to `*s.0`, because the type `Scribble<'_>` implements the `Drop` trait
   |
   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future

warning[E0713]: borrow may still be in use when destructor runs
  --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:75:5
   |
LL | fn boxed_boxed_scribbled<'a>(s: Box<Box<Scribble<'a>>>) -> &'a mut u32 {
   |                          -- lifetime `'a` defined here
LL |     &mut *(**s).0 //[nll]~ ERROR borrow may still be in use when destructor runs [E0713]
   |     ^^^^^^^^^^^^^ returning this value requires that `*s.0` is borrowed for `'a`
...
LL | }
   | - here, drop of `s` needs exclusive access to `*s.0`, because the type `Scribble<'_>` implements the `Drop` trait
   |
   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future

error: compilation successful
  --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:82:1
   |
LL | / fn main() { //[ast]~ ERROR compilation successful
LL | |      //[migrate]~^ ERROR compilation successful
LL | |     let mut x = 1;
LL | |     {
...  |
LL | |     *boxed_boxed_scribbled(Box::new(Box::new(Scribble(&mut x)))) += 10;
LL | | }
   | |_^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0713`.